The Accuracy 1st Scope Level is just as it sounds, a leveling device that mounts to your scope. The further the distance we shoot, the more important it is to keep our reticle perfectly vertical with gravity. The Accuracy 1st Development Group scope level was designed to achieve precise resolution of less than 1° with line increments of 2.5°. The ceramic ball inside the vile won't change size with temperature and density altitude like an air bubble will. Typically air bubble levels require 3° to 5° to even register movement; however, the Accuracy 1st custom level will read movement at a minimum of 1° and will extend measurements out to +/- 10°.